Production of metallic magnesium



Jan. 16, 1934. w F. HANSGIRG 1,943,601

PRODUCTION OF METALLIC MAGNESIUM Filed Feb 21. 1951 My 0 C C001 nmnoaen ran .wac/r CHILL/N6 AND ronmua m unz man/mun POWDER CONDENSER PREHEA rm EL ECTR'C MAGNESIUM VAPOR "mama? FURNACE cARao/v Mouoxme" (SHOCK wot/N6) AND lMPUR/TIES.

GAS WITH ENTRAINED FINELY DIV/D50 HA6- NESIUM NWDFR AND 'IHPURITIES uvonaazu v D/sT/LLAT/ON FURNACE SEPA RA ran AND IMPURITIES N (nsaucsa Prensa/vs) .ififif w MONOXIDE P U 2 E ma Mrs/un- DIS TILLA TE AND HYDROGEN COMPACT MAGNESIUM 0F HIGH Puz/rr WITNESSES INVENTOR 1/4 a. 425% fiMJZZJM Patented Jan. 16, 1934 UNITED STATES PRODUCTION OF METALLIC MAGNESIUM Fritz Hansgirg, Radenthein, Austria, assignor to American Magnesium Metals Corporation, Pittsburgh, Pa., a corporation of Delaware Application February 27, 1931, Serial No. 518,915, and in Austria August 4, 1930 9 Claims.

This invention relates to the production of metallic magnesium.

Heretofore one method of producing magnesium involved the volatilization of the magnesium by treating magnesium containing material, such as magnesium oxide, mixed with a reducing agent, such as coke. In one type of process the magnesium oxide was formed up with coke in the shape of an electrode which was used in a high tension arc. The magnesium vapors which were formed were entrained in and removed by the gas flow from the reaction chamber and condensed in a condensation section of the apparatus. This type of process involved in- 1 herent disadvantages. The magnesium vapor condensed out in the form of fine metal drops which were rapidly oxidized, under the influence of the combustion gases, to form a thin and rather adherent coat of the oxide upon the surface of the metal. This formation of the oxide film substantially prevented the fusion or coalescence to larger masses and hence precluded the immediate recovery of the metal in compact form. These types of processes also involved a subsequent remelting of the magnesium dust. This was likewise rendered difilcult due to the coating of the oxide. In such processes, therefore, it was customary to avoid the formation of dust as much as possible by cooling the magnesium vapor gradually down to the liquefaction temperature.

According to the present process metallic magnesium in relatively compact and massive form may be readily obtained by a novel type of treat.- ment, departing in essential features from the prior art methods.

It is, therefore, an object of the present invention to provide a novel process to produce compact metallic magnesium.

Another object is to provide an improved and efficient method of preparing magnesium, in which formation the magnesium oxide is substantially minimized.

Yet a further object is to provide a process for producing metallic magnesium in a purified form.

With these and other equally important objects in view the invention comprehends the concept of volatilizing magnesium in the presence of a non-oxidizing gas and then suddenly cooling or shock chilling the vapor so as to produce magnesium in solid and discrete form. The discrete form of metal thus produced is preferably. distilled or revaporized under reducing conditions 55 and under reduced pressure and temperature conditions so controlled as to extract the magnesium largely free from foreign substances, such as iron and silicon. With this type of process it is found that the particles of magnesium vapor readily coalesce or agglomerate to form the compact massive metal. With this process magnesium metal of very high purity is obtained.

In the drawing a flow sheet illustrating the steps of the operation is shown.

With the major concepts in mind it will be 55 appreciatedthat a number of modified forms of processes may be employed within the scope of the invention. According to one preferred method the magnesium containing material, such as magnesium oxide, is crushed or ground and is mixed with a finely divided reducing agent such as coke. If desired, the magnesium containing' material may be mixed with powdered or finely divided carbon and the mass bonded with suitable binding substances, such as tar oil, tar, pitch, molasses, asphalt and asphaltemulsions, etc. This mass may be briquetted and heated to temperatures sufliciently high to insure the carbonization or coking of thebinder. The carbonization products thus obtained may 30 be finely ground.

The mixture of magnesium containing material and carbon, whether prepared by the method described or by any other suitable-method, is preferably blown into the zone of action of a high tension electric arc. Preferably within the zone of thermal decompositionreducing conditions are'ma'intained. This may be done by either blowing in preheated hydrogen with the raw material or by maintaining an atmosphere of highly heated hydrogen in the decomposition zone. The hydrogen employed in the process is preferably preheated; as for example by passing it in a heat exchange relationship with the efiluent combustion gases.

While it is preferable to rapidly raise the magnesium containing material to the volatilization temperature, by passing the raw material immediately into a high temperature zone, it is to be understood that the invention is not restricted to this particular step. Advantageous results may be obtained by charging a mass of the raw material and coke to a furnace and heating the whole mass by means-of an electric are or by tlon. As noted hereinbefore, in the older processes of this type the condensation of the magnesium was secured by a gradual diminution in temperature. According to the present process, however, the temperature of the magnesium is very rapidly reduced so that it passes from the vapor phase very rapidly to the solid phase, without the protracted period of transition through the liquid phase, as in the case of prior processes.

This sudden chilling or shock cooling may be obtained in a number of specific manners. One method comprises subjecting the magnesium vapors to the action of chilling agents, such as cooled indifferent gases. A preferred material for thls purpose is cooled hydrogen which may be blown into the condensation chamber so as to intimately contact with the dispersed magnesium vapor. In lieu of using chilled hydrogen the magnesium vapor may be caused to impinge upon extensive cooled surface areas. By reason of this sudden drop in temperature the formation of magnesium dust or finely divided solid magnesium 1s promoted and at the same time the re-oxidation, causing the formation of an oxide coating on the surface of the metal grains, is reduced because of the great chilling rapidity.

The gaseous stream may be withdrawn from the condensing chamber and the entrained finely divided magnesium powder may be separated from the gases in any desired manner, as for example by passing the gas through suitable fil ters, centrifugal separators, etc.

After the finely divided magnesium has been obtained in the manner described, it is then treated to reduce it to a compact or massive form. In the preferred modification this is accomplished by subjecting the finely divided magnesium to vaporization or distillation under reduced pressure and preferably in an atmosphere of a non-oxidizing or indifferent gas, such as hydrogen. By distilling the magnesium under reduced pressure, it will be appreciated, the vaporization may be effected at a lower temperature. In operating the process the distillation temperatures are preferably accurately controlled so as to drive over only the magnesium vapor and to retain in the distillation vessel or retort the undesired foreign substances, such as iron, silicon, aluminum, calcium, etc. Under these conditions, namely reduced pressure distillation in the presence of hydrogen, the magnesium is removed from any oxide which may have been formed by, so-to -speak, local distillations. The magnesium vapor driven off is passed to a condensing section and preferably condensed in an atmosphere of hydrogen. It will be appreciated that while operating in this manner, namely in two stages, the magnesium vapor which is driven off in the second distillation step is, soto-speak, in a highly concentrated form as distinguished from the dilute or dispersed condition, as in the case of the initial volatilization from the raw materials. It is also to be observed that the distillation step serves in effect as a purifying step because, by reason of the temperature control, a fractional distillation of the magnesium maybe attained so that the magnesium is not contaminated with the impurities mentioned.

The nature of the process permits of a wide flexibility in operation. The two steps may be carried out separately and with any desired time interval, or the process may in fact be made continuous by passing the magnesium dust from the separating element directly to a retort. Since, in the preferred process, the initial volatilization may be carried out with small batches, economies of operation are permitted because of the opportunity to operate the high temperature are at the low load period.

In carrying out the operations the hydrogen employed in the first and second stages may be recycled so as to insure maximum economy by reuse. As noted hereinbefore, operating efficiencies may be enhanced by preheating the hydrogen employed in the volatilization furnace and/ or in the distillation stage.

While I have used the term inert gas in the specification, and mentioned hydrogen gas, the remarkable effectiveness of the operation leads me to believe that the hydrogen gas may perform a real reducing function. At the temperatures at which the operation is conducted, and in the presence of an electric are, there may be a tendency for the molecular hydrogen to be changed to the atomic state, which may account for some of the unexpectedly excellent results obtained. It is to be understood that I am not to be bound by this theory of operation, but it does tend to explain economies otherwise unobvious. Where the expression reduced pressure is used, this is employed to mean any pressure substantially below atmospheric.

As an alternative operation the metallic powder formed can be treated at such a temperature in a reducing or inert atmosphere, as in an atmosphere of hydrogen, that the small particles fuse or liquefy, and the finely divided magnesium powder flows or coalesces together as a liquid metal. It is to be understood that this temperature must be in any case above the melting point of metallic magnesium, that is, 650 0., but below its boiling temperature. The boiling temperature can be lowered by reducing the pressure, and it is contemplated that this coalescing step can be performed at a reduced pressure, taking care that the temperature at such reduced or subnormal pressure is not high enough to cause boiling of the coalesced magnesium mass.

While a preferred process has been described, it is to be understood that this is given merely as one operative embodiment of the major principles hereinbefore described; and since 'these may be incorporated in other specific processses it is not intended to be limited to the fidiscribed, except as such limitations are clearly omprehended in the spirit of the appended clainrs.

I claim:

1. A process of producing magnesium which comprises extracting magnesium in finely divided form from its compounds and then distilling the thus formed magnesium under reduced pressure and in contact with an indifferent gas.

2. A process of producing magnesium which comprises volatilizing magnesium from magnesium containing material and recovering magnesium in discrete form; then distilling the discrete form of the magnesium under reduced pressure and in the presence of hydrogen and condensing the vapor to compact metallic magnesium.

3. A process of producing magnesium which comprises evolving magnesium vapor from magnesium containing material by thermal reduction in the presence of hydrogen, then shock cooling the vapors to produce magnesium in finely divided form, and then distilling the flnelyrdivided magnesium under reduced pressure and in the presence of hydrogen and condensing the magnesium vapor to the compact form.

4. A process of producing magnesium which comprises evolving magnesium vapor from magnesium containing material by thermal reduction in the presence of hydrogen, then shock cooling the vapors by contacting them with cooled hydrogen, to produce solid magnesium in finely divided form; then distilling the finely divided magnesium under reduced pressure and in the presence of hydrogen and condensing the magnesium vapor to a compact form.

5. A process of producing magnesium in compact form which comprises suddenly evolving magnesium vapor from magnesium containing material, then shock cooling the magnesium vapor in the presence of hydrogen to transform the vapors to discrete solid particles; then heating the particles under reduced pressure and in the presence of hydrogen to distill off the magnesium and condensing the magnesium in compact form.

6. A process of producing magnesium in compact form which comprises blowing a powdered mixture of magnesium containing any carbonaceous material into the zone of action of an electric arc, then shock cooling the evolved vapors in the presence of hydrogen; separating the finely divided solid magnesium from the combustion gases and then heating the solid magnesium to distillation temperatures under reduced pressure and in the presence of hydrogen and condensing the vaporized-magnesium in a non-oxidizing atmosphere.

'7. A process of producing magnesium in compact form which comprises blowing a powdered mixture of magnesium-containing and carbonaceous material into the zone of action of an electric arc; maintaining an atmosphere of hydrogen within said zone of action; then shock cooling the vapors of magnesium by subjecting it to the action of a cooling agent unreactive with metal-' lic magnesium; separating the finely divided solid magnesium from the reaction gases; then subjecting theso formed magnesium to a reduced pressure distillation in the presence of hydrogen in which distillation the temperature is so controlled as to separate the magnesium from contained impurities and then condensing the magnesium vapors to a compact form.

8. A process of producing magnesium which comprises extracting magnesium in the form of vapor from its compounds, condensing the magnesium to produce solid magnesium in finely divided form and then distilling the thus formed magnesium under reduced pressure and in contact with an indifierent gas.

9. A process of producing magnesium which comprises extracting magnesium in the form of vapor from its compounds by means of a carbonaceous reducing agent, condensing the magnesium to produce solid magnesium in finely divided form and then distilling the thus formed magnesium under reduced pressure and in contact with an indifierent gas and recondensing the magnesium.

FRITZ HANSGIRG.

CERTIFICATE or CORRECTION;

Patent No.- 1,943, 601.

January 16, 1934.

ram HANSGiRG.

it is hereby certiiied that error appears in the printed specification of the above numbered patent requiring correction as follows: a, ior "any" read and; and that the said Letters Patent should be read with this Page 3, line 20, claim correction therein that the same may conform to the record of the case in the Patent Giiice.

Signed and sealed this 6th day of March, A. D. 1934.

I (Seal) F. M. Hopkins Acting Commissioner 0i Patents. 

